Direct production of olefins from syngas with ultrahigh carbon efficiency

Syngas conversion serves as a competitive strategy to produce olefins chemicals from nonpetroleum resources. However, the goal to achieve desirable olefins selectivity with limited undesired C1 by-products remains a grand challenge. Herein, we present a non-classical Fischer-Tropsch to olefins process featuring high carbon efficiency that realizes 80.1% olefins selectivity with ultralow total selectivity of CH4 and CO2 (<5%) at CO conversion of 45.8%. This is enabled by sodium-promoted metallic ruthenium (Ru) nanoparticles with negligible water-gas-shift reactivity. Change in the local electronic structure and the decreased reactivity of chemisorbed H species on Ru surfaces tailor the reaction pathway to favor olefins production. No obvious deactivation is observed within 550 hours and the pellet catalyst also exhibits excellent catalytic performance in a pilot-scale reactor, suggesting promising practical applications.

conversion rates and high carbon efficiency is one of the biggest challenges in syngas chemistry. The excellent, high-quality work by Yu et al. reported in this manuscript represents a significant step forward in this direction. The authors employed a novel Na-promoted Ru/SiO2 catalyst to realize the direct conversion of syngas to olefins (STO), especially to long chain C5+ olefins, with an outstanding olefins selectivity of up to 80.1% and a remarkably ultralow selectivity (< 5%) to unwanted C1 by-products (CH4, CO2) at relatively high CO conversion (> 45%). The Na-Ru/SiO2 catalyst features high stability with no signs of deactivation during at least 550 h on stream and exhibits excellent catalytic performance when tested in the form of cylindrical-shaped pellets under industrially relevant conditions and therefore with good prospects for practical application. The outstanding STO performance displayed by the Na-Ru/SiO2 catalyst is ascribed to an increased electronic density of surface metallic Ru atoms due to electron transfer from the Na promoter (supported by XPS, CO-DRIFTS, and DFT) strengthening the CO adsorption capacity of the Ru sites, along with a reduced surface mobility of chemisorbed H species suppressing secondary hydrogenation of olefins. A further differential aspect of the Na-Ru/SiO2 catalyst with respect to most current STO catalysts is its negligible activity for the competing WGS reaction resulting in an unusually ultralow CO2 selectivity (< 3%) even at CO conversions as high as 68%. The discussions and conclusions of this study are well supported by experiments and advanced spectroscopic and microscopy characterizations of the catalysts at different stages.
Overall, this is an excellent work deserving publication in Nature Commun. I only have a few comments that the authors should address before its definitive acceptance for publication.
1. As correctly stated by the authors, further studies would be required to achieve a more effective use of Ru in the Na-Ru/SiO2 catalyst in order to decrease its cost and thereby to enhance its economic viability. In this respect, I am wondering why the catalyst was reduced at the high temperature of 723 K in spite the H2-TPR profiles indicate the complete reduction of RuO2 to metallic Ru at temperatures below 500 K (Fig. S11). In principle, one might expect a higher Ru dispersion and therefore a more efficient metal utilization at lower reduction temperatures.
the Fischer-Trospch to Olefins (FTO) technology. They highlighted the suppression of undesired C1 products (CO2 and CH4) to <5 % which leads to 80 % olefins selectivity at 46 % CO conversion. The robustness of the catalytic performance is thoroughly investigated, through the screening of various process parameters including temperature, pressure, H2/CO ratios and space velocity. In addition to the steady-state catalytic performance, transient and co-feeding experiments were performed to probe the reactivity of the catalysts for ethene hydrogenation and water-gas-shift. Last but not least, the authors also utilized multiple analysis tools to identify catalyst properties which substantiated their findings. The authors deserve compliments for the high quality and detailed presentation of their results, and their meticulous design of experiments. The direct conversion of synthesis gas to olefins facilitates a more sustainable production of chemicals from alternative feedstocks, leading to a circular carbon economy. Hence, a significant advancement would be valuable to the scientific community and society, warranting a spot in Nature Communication. In this case, the authors justify the importance of their work by reasoning that the olefins yields attained with their Na-promoted Ru/SiO2 catalysts surpassed all state-of-art catalysts. The concept of suppressing C1 production is first proposed by Xie et al. (ref. 14) using Co-based catalysts and later by Xu et al. (ref. 10) using Fe-based catalysts so this is not new. Na promotion on Ru-based catalysts have been concluded to promote olefins production (ref. 21 and Williams and Lambert 2000, 10.1023/A:1019023418300) so this aspect is also supported by literature. However, there has been negligible progress on Ru-based catalysts, and this work brings awareness and encourages the exploration of Ru-based catalysts for olefins production with limited C1 production. Hence, this work is recommended for publication in Nature Communication if the following scientific points could be clarified/ improved. 1. Line 21 '… oligomerization of lower olefins lead to high value-added long-chain olefins via Ziegler-Natta polymerization process.' The olefins produced is in the range of C2-C20, so the alternative commercial process should be the Shell Higher Olefins Process (e.g. Kiem 2013, 10.1002/anie.201305308) instead of Ziegler-Natta polymerization. 2. The significance of this work is arguably over-stated and over-simplified. Most state-of-art FTO catalysts focus on the selectivity of C2-C4 olefins and the olefins selectivity in the C5+ products is not specified. However, this does not mean that the C5+ fraction did not contain olefins, as the author inaccurately suggested in Figure 1a. For instance, the Co1Mn3-Na2S catalysts showed <7 % C1 products at 240 °C and 10 bar with olefin/paraffin ratio of ~ 5 (Figure 3a in ref. 14). This suggests that the olefins selectivity of the Co1Mn3-Na2S catalysts (~70 %) is closer to the Na-Ru/SiO2 catalysts than the authors depicted in Figure 1a and stated in line 68-69. The authors are recommended to go through the literature in detail to make an accurate comparison. Another point is that although the selectivity towards olefins was high, the carbon distribution remained broad due to ASF so the selectivity of each olefins was ≤10 %. Hence, it is perhaps too general to state that the C5+ olefins are of value. Instead, the authors could specify the selectivity towards certain fraction of value, e.g. C2-C4 olefins for bulk chemicals, C12-C18 for detergents (Kiem 2013). 3. Stability tests shown in Figure 1e and S1 are for Na-2%Ru(P)/SiO2 catalyst but all other catalyst test results are compared using Na-Ru/SiO2 and Ru/SiO2 catalysts. Representative stability tests for Na-Ru/SiO2 and Ru/SiO2 catalysts should be added. 4. In FTS and FTO processes, product selectivity is dependent on conversion so product selectivity should be compared at similar conversion levels. For Co-based and Ru-based catalysts, CH4 selectivity is shown to increase when CO conversion is >80 % (Yang et al. 2014(Yang et al. , 10.1016(Yang et al. /j.apcata.2013. Conversion results should be added to Figure 1 and S3 to demonstrate that the lower C1 selectivity attained by Na-Ru/SiO2 was not due to a difference in conversion. 5. Line 178-179 'Specially, the homogenous distribution of Na over the catalyst surface may benefit the strong electronic interaction between Ru NPs and Na.' This is doubtful, because one would think that Na has to be in contact with the Ru NPs (i.e. Figure S10) to promote the Ru active sites and the Na species on the support acted as spectators. From the various characterization data, could the authors (semi)quantify the amount of Na on the support vs. on Ru NPs? This would clarify the role of Na when it is on the support vs. Ru NPs. The authors are further suggested to include HAADF-STEM images and EDX elemental mapping of the spent Ru/SiO2 and 2Na-Ru/SiO2 catalysts so as to check for the sensitivity of the Na signal and to prove the above sentence. The experimental loading of Na measured by ICP-OES should also be included. 6. Line 198-199 'Based on the linear characteristic of ASF distribution, we can infer that the surface carbide mechanism …' This is not so accurate, because the linearity of the ASF distribution is a characteristic of the FTS and FTS technologies, regardless of surface carbide/ bulk carbide/ CO insertion mechanisms etc. The authors could perhaps refer to computational studies on Ru-based FTS catalysts by the group of Hensen (10.1039/c4cy00483c and 10.1002/anie.201406521) to strengthen their mechanism discussion. 7. Line 265-268 regarding the discussion on the WGS activity of Na-Ru/SiO2. The authors failed to acknowledge that metallic Ru-based FT catalysts, similar to the metallic Co-based catalysts (in ref. 14), have negligible WGS activity at low/ moderate CO conversion levels. In Figure 1f, Ru/SiO2 had no WGS activity and the WGS activity actually increased with increasing Na loading. The authors should clarify that the WGS activity increased with Na promotion and provide a possible explanation on why Na promotion increased WGS activity and what are the possible implications. 8. Line 471-472 regarding the scale-up operation. In the microreactor, plug-flow conditions appear to be fulfilled (reactor inner diameter >10 times catalyst particle sieve fraction, catalyst bed height >50 times catalyst particle sieve fraction). However, this does not appear to be the case for the pilot-scale reactor as the reactor inner diameter was only 4 to 6 times the dimensions of the extrudate. To demonstrate the success of the scale-up operation to claim 'industry-relevant testing', the pilot-scale reactor should also be operated under plug flow conditions and a direct comparison of the Na-2%Ru(P)/SiO2 catalyst performance in the microreactor and the pilot-scale reactor would be appreciated. 9. Spelling mistakes: line 78 ('predicated' = predicted), line 250 ('specular' = speculated), line 421 ('stand' = standard) 10. Experimental methodology for x-ray spectroscopies is missing?
Reviewer report by Jingxiu Xie 1

Comments:
In this manuscript, the authors developed an active Na-Ru/SiO2 catalyst for production of olefins from syngas. An enhanced olefin selectivity with limited selectivity of CH4 and CO2 was obtained by using the Ru-based catalyst, which usually favored the production of long-chain saturated hydrocarbons. The addition of sodium made a significant change in product selectivity, which was probably originated from the hydrogenation ability. The authors employed various characterizations and probe experiments to verify the hypothesis. This is an interesting work with good organization.
After some revisions, this work can be published in Nature Communications.
Below are some suggestions: Author reply: Thanks a lot for your valuable comments. The point-by-point responses to your comments are shown as follows:

Comments:
1. In this work, the authors mainly compared the performance between Ru/SiO2 and Na-Ru/SiO2, but stability test was conducted on Na-2%Ru(P)/SiO2. The authors would better give an explanation to the employment of Na-2%Ru(P)/SiO2 the first time it appeared in Fig 1E. Besides, what about the stability of Ru/SiO2? Author reply: Thank you for your professional comment. The catalytic stability of Ru/SiO2 and Na-Ru/SiO2 catalysts with 5 wt.% of Ru were compared and showed in Supplementary Fig. 2. Both Ru/SiO2 and Na-Ru/SiO2 catalysts showed high stability within 50 h of test. To better illustrate the outstanding FTO catalytic performance of Na promoted Ru-based catalyst, the preparation method was optimized, and a Na-2%Ru(P)/SiO2 catalyst with a relative lower Ru loading amount was prepared for FTO evaluation. Polyvinylpyrrolidone (PVP) was used during catalyst preparation procedure to greatly increase the Ru metal dispersion with higher exposed metallic surface area.
It was found that the Na-2%Ru(P)/SiO2 catalyst showed high stability for 500 h, and olefins selectivity kept in the range of 75~80% while that of the undesired C1 byproducts was always suppressed within 5%. 2 In the revised manuscript, the stability test of Ru/SiO2 and Na-Ru/SiO2 catalyst was added as Supplementary Fig. 2 in the Supplementary Information, and the corresponding explanation was added in the main text as following: "Furthermore, stability test was carried out as shown in Supplementary Fig. 2. The catalytic performance for both Ru/SiO2 and Na-Ru/SiO2 catalysts remained stable within 50 h of test. Especially, the Na-2%Ru(P)/SiO2 catalyst with much lower Ru loading amount (1.8 wt.% Ru, ICP) exhibited high stability for 500 h without any significant loss in activity and selectivity. Overall, the activity remained at around 0.700 molCO·gRu -1 ·h -1 with intrinsic TOF of 0.210 s -1 , and olefins selectivity in total products kept in the range of 75~80% while that of undesired C1 by-products was always suppressed within 5% ( Author reply: Thanks for your valuable comment. The catalyst activity did change significantly after the introduction of Na promoter. Such phenomena are also commonly observed for metallic Co-based FTS catalyst, and it is always believed that the alkali metal exhibits negative effect on FTS activity. Several explanations have been put forward for the behavior of alkali promoter, i.e., electronic effect, site blocking effects,

A B
3 and blocking of specific sites of importance for hydrogen adsorption and dissociation (Catal. Today, 2013,215, 60;Chin. J. Chem. 2017, 35, 918). In this work, the detailed structure difference between Ru/SiO2 and Na-Ru/SiO2 were characterized for comparison study. Structure characterization by XRD/HRTEM/XAFS/XPS in Fig. 2 and Supplementary Fig. 7 -10 suggested that the Na doping did not change the Ru phase, and metallic Ru phase exclusively existed for both Ru/SiO2 and Na-Ru/SiO2.
However, a significant electronic effect was observed after introducing Na promoter according to XAFS/DRIFTS/XPS, and an electron-rich Ru centers for Na-Ru/SiO2 sample was observed, along with the observation of increased CO adsorption strength.
The strongly adsorbed CO* molecules will occupy a large amount of exposed metallic In the revised manuscript, some sentences were revised for better understanding in Paragraph 4 of "Results and discussion": "We speculate that the possible reason for the huge difference in catalytic performance of Ru/SiO2 and Na-Ru/SiO2 including activity and selectivity may lie in the discrepancy of dynamic of chemisorbed hydrogen"; "Based on these discussions, it is reasonable to speculate that the Na promoter could decrease the fraction of Ru surface sites available for H2 adsorption and reduce the mobility of chemisorbed H2, thus decreasing the reactivity of H2 and hydrogenation capacity of Ru-based FTS catalysts and rending them very efficient for unsaturated olefins production with limited CH4 selectivity. In addition, the suppressed reactivity of chemisorbed H2 may also lead to the decrease in catalytic activity." 3. H2-TPR results suggested that the addition of Na retarded the reduction of RuO2, but from XAS and XPS spectra, the Na-Ru/SiO2 showed a slightly higher reduction degree of Ru than Ru/SiO2. Did the H consumption vary with sodium addition? The authors would better give some explanations to the higher electron density in Na-Ru/SiO2.
Author reply: Thanks for your valuable comment. According to the reviewer's comments, we calculated the apparent H2 consumption through the H2-TPR results. As shown in Table 1(for response), the addition of Na slightly increased the apparent H2 consumption. The apparent hydrogen consumption was calculated according to the following equation (Journal of Catalysis, 1988, 111(1): 59-66.) Apparent hydrogen consumption = Reduction + Adsorption + Spillover -

Desorption of chemisorbed hydrogen -Desorption of spillover hydrogen
In the view of the complexity of the factors involved and the significant H2 spillover-effect of Ru metal, it is difficult to calculate the actual H2 consumption for reduction process alone. The increased apparent H2 consumption for Na-Ru/SiO2 was mainly caused by the improved metallic Ru dispersion (Supplementary Table 7) and  In this work, all catalysts were reduced at 723 K for 4 hours under a flow of H2 before reaction, and both Ru/SiO2 and Na-Ru/SiO2 could be reduced completely under above reduction conditions according to H2-TPR profiles. From XAS and XPS spectra, the exclusive metallic Ru species in both Ru/SiO2 and Na-Ru/SiO2 were identified. The slight shift in XANES was due to the electron-donor effect of sodium. The increased electronic density of Ru center for Na-Ru/SiO2 can clearly be confirmed by XPS and CO-DRIFTS spectra, as shown in Fig. 2E, respectively. Furthermore, the Bader charge analysis based on DFT calculations demonstrated the electron-rich of surface Ru metal species after loading Na ion on the Ru (0001) surface ( Supplementary Fig. 13), which strengthened CO adsorption and resulted in a CO-rich and H2-poorn local chemical environment that benefits FTO performance.

From the experimental section, I found that XPS spectra were ex-situ conducted.
Why there was no Ru δ+ detected as shown in Fig 2E? Author reply: Thanks for your professional comment. As indicated by the reviewer, the XPS spectra were collected under ex-situ condition. Actually, a passivation treatment with 1 vol% O2/Ar was specially performed for these catalysts. In order to remove adsorbate and oxide layer, we employed the argon ion etching method during the exsitu XPS experiment. We are sorry that the relative experimental detail was not presented in the original manuscript. We have revised it and more details were added in the part of experimental methods.
In addition, we compared the XPS spectra of sample without argon ion etching treatment process. The corresponding fitting spectra results are shown in Fig.1(for response). The presence of an oxidation state of Ru species was observed on the reduced 6 Ru/SiO2 and Na-Ru/SiO2 catalysts surface due to passivation treatment, and the peaks at 280.9 eV and 280.7 eV were assigned to Ru δ+ species (J. Mater. Chem. 2012, 22, 14944-14950;J. Am. Chem. Soc. 2018, 140, 4172-4181).

Ru/SiO2 catalysts without argon ion etching treatment process.
In the revised manuscript, the detailed XPS experiment method was added: "X-ray photoelectron spectroscopy (XPS) was obtained by Thermo Fisher Scientific K-Alpha spectrometer equipped with the Al Kα (1486.6 eV) radiation source.
Before XPS measurement, the sample was treated by argon ion etching to remove surface adsorbate and oxide layer. The results were calibrated by setting the C 1s peak of 284.8 eV."

When compared with previously reported catalysts, the authors should pay
attention to the reaction conditions. The authors would better provide the performance of Na-Ru/SiO2 conducted at different conditions. And reaction rates of the catalysts should be included in Table S1. The catalytic performance of Na-Ru/SiO2 conducted at different reaction conditions including ratios of H2/CO (Fig. 1C), space velocities (Fig. 1D), reaction temperatures ( Supplementary Fig. 6), and reaction pressures (Supplementary work.
Author reply: Thank you for your valuable comment. We agree with the reviewer that a DFT simulation for olefins production will greatly improve the quality of this work.
It is well known that Fischer-Tropsch synthesis is a complex reaction and it remains a great challenge to elucidate each reaction step. According to the widely accepted surface carbide mechanism, the key steps for olefins production are the hydrogenation or β-hydride abstraction of surface intermediate to terminate the carbon chain growth.
The secondary hydrogenation of olefins intermediates is another vital step for olefins production. Based on these analyses, we have calculated and compared the energies for ethylene adsorption on Ru (0001) and Na2O/Ru (0001)

Minor suggestions:
(1). Generally, there are no citations included in the abstract.
(2). The font sizes in a figure should be kept the same. Pay attention to the font sizes in Fig 2 and Fig3. (3). Symbols used in this manuscript should be carefully checked, such as "mL", "C 1s", etc.
Author reply: Thanks for your valuable comment.
(1) The abstract has been rewritten with no citations as follow: "Syngas conversion serves as a competitive strategy to produce olefins chemicals from nonpetroleum resources. However, the goal to achieve desirable olefins selectivity with limited undesired C1 by-products remains a grand challenge. Herein, we present a non-classical Fischer-Tropsch to olefins process featuring high carbon efficiency that realizes 80.1% olefins selectivity with ultralow total selectivity of CH4 and CO2 (< 5%) at CO conversion of 45.8%. This is enabled by sodium-promoted metallic ruthenium (Ru) nanoparticles with negligible water-gas-shift reactivity. Change in the local electronic structure and the decreased reactivity of chemisorbed H species on Ru surfaces tailored the reaction pathway to favor olefins production. No obvious deactivation was observed within 550 hours and the pellet catalyst also exhibited 11 excellent catalytic performance in a pilot-scale reactor, suggesting promising practical applications." (2) We have corrected the font size in Fig. 2 and Fig. 3, and we also checked the other Figures and make sure the same font size was applied.
(3) We have checked the symbols used in manuscript carefully and addressed this issue in the revised manuscript and supplementary information. 12

Reviewer #2
Comments: Achieving the selective production of specific valuable hydrocarbons directly from syngas at high CO conversion rates and high carbon efficiency is one of the biggest challenges in syngas chemistry. The excellent, high-quality work by Yu et al.
reported in this manuscript represents a significant step forward in this direction. The authors employed a novel Na-promoted Ru/SiO2 catalyst to realize the direct conversion of syngas to olefins (STO), especially to long chain C5+ olefins, with an outstanding olefins selectivity of up to 80.1% and a remarkably ultralow selectivity (< 5%) to unwanted C1 by-products (CH4, CO2) at relatively high CO conversion (> 45%).
The Na-Ru/SiO2 catalyst features high stability with no signs of deactivation during at least 550 h on stream and exhibits excellent catalytic performance when tested in the form of cylindrical-shaped pellets under industrially relevant conditions and therefore with good prospects for practical application. The outstanding STO performance displayed by the Na-Ru/SiO2 catalyst is ascribed to an increased electronic density of surface metallic Ru atoms due to electron transfer from the Na promoter (supported by XPS, CO-DRIFTS, and DFT) strengthening the CO adsorption capacity of the Ru sites, along with a reduced surface mobility of chemisorbed H species suppressing secondary hydrogenation of olefins. A further differential aspect of the Na-Ru/SiO2 catalyst with respect to most current STO catalysts is its negligible activity for the competing WGS reaction resulting in an unusually ultralow CO2 selectivity (< 3%) even at CO conversions as high as 68%. The discussions and conclusions of this study are well supported by experiments and advanced spectroscopic and microscopy characterizations of the catalysts at different stages. Overall, this is an excellent work deserving publication in Nature Commun. I only have a few comments that the authors should address before its definitive acceptance for publication.
Author reply: Thank you very much for your valuable comments. The point-by-point responses to your comments are shown as follows： 13 Comments: 1. As correctly stated by the authors, further studies would be required to achieve a more effective use of Ru in the Na-Ru/SiO2 catalyst in order to decrease its cost and thereby to enhance its economic viability. In this respect, I am wondering why the catalyst was reduced at the high temperature of 723 K in spite the H2-TPR profiles indicate the complete reduction of RuO2 to metallic Ru at temperatures below 500 K (Fig. S11). In principle, one might expect a higher Ru dispersion and therefore a more efficient metal utilization at lower reduction temperatures.
Author reply: Thanks for your valuable suggestions. The utilization efficiency of noble Ru metal is a key factor that influences its future industrial application, and more studies are required for Na-Ru/SiO2 catalytic systems. We agree with the reviewer that the reduction temperature plays a significant role in affecting the Ru dispersion and metal utilization efficiency. According to the hint of reviewer, the dispersion of metallic Ru for Na-Ru/SiO2 catalyst under different reduction temperatures were calculated. As shown in Table 2(for response), a higher Ru dispersion was obtained at lower reduction temperature as expected. and Na-Ru/SiO2. In the follow-up research, we will continue to comprehensively study the effect of reduction temperature on structure-performance relationship of Na-Ru/SiO2 cases. Strategies to improve the metal utilization efficiency is also a continuous 14 on-going research work.

P10L227: "It was suggested that the Na promoter might increase the "internes"
of adsorbed H and suppress the secondary hydrogenation of olefins". What does "internes" mean? Probably the authors meant "inertness". Please, clarify it.
Author reply: Thanks for your valuable suggestions. We are sorry for the incorrect spelling, and we have corrected it as "inertness" in the revised manuscript.
Author reply: Thanks for your valuable suggestions. We are sorry for the incorrect spelling, and we have corrected it as "speculate" in the revised manuscript.  Author reply: We gratefully appreciate for your professional comment. According to your suggestion, the sentence of "via Ziegler-Natta polymerization process" has been deleted in the revised manuscript and references mentioned by the reviewers were cited.

state-of-art FTO catalysts focus on the selectivity of C2-C4 olefins and the olefins
selectivity in the C5+ products is not specified. However, this does not mean that the C5+ fraction did not contain olefins, as the author inaccurately suggested in Author reply: We gratefully appreciate for your professional comment. We sincerely apologize for neglecting to label the selectivity to lower olefins (C2-4 = ) in Fig. 1A. This 17 may cause some misunderstanding to the readers and reviewers. In Fig. 1A in the revised manuscript, we have made notation to these cases reporting lower olefins (C2-4 = ) selectivity.

Fig. 1A. Catalytic performance for direct syngas conversion to olefins. (A)
Comparison of catalytic performance among Na-Ru/SiO2 and other previously reported catalysts [7][8][9][10][11]13,15 . (a: C2-4 = selectivity) In addition, we agree with the reviewer that the importance of focusing on selectivity of certain carbon number of olefins. According to the data shown in Fig.1B, the olefins distribution with certain carbon number range is showed in Supplementary   Fig. 1. We also added some description in the revised manuscript as follows: "Specially, the fraction of value-added C5-C11 α-olefins was as high as 57.8%, which can be used for production of high-quality lubricant, plasticizer and surfactant, while the fraction of detergent-range C12-C18 α-olefins reached 16.4% ( Supplementary   Fig. 1)."

"Supplementary Notes:
The Na-Ru/SiO2 catalyst exhibits a narrower carbon distribution compared with the classical FT catalysts. The fraction of lower olefins (C2-4 = ) accounts for 25.5%, which is commonly used for bulk chemicals. While the fraction of C5-C11 olefins reaches 57.8%, and can be widely used as raw materials and/or intermediates for production of chemicals such as lubricant, plasticizer and surfactant. In addition, the C12-C18 slate olefins with fraction of 16.4% favors the production of detergent." Figure 1e and S1 are for Na-2%Ru(P)/SiO2 catalyst but all other catalyst test results are compared using Na-Ru/SiO2 and Ru/SiO2

catalysts. Representative stability tests for Na-Ru/SiO2 and Ru/SiO2 catalysts should be added.
Author reply: Thank you for your professional comment. The catalytic stability of Ru/SiO2 and Na-Ru/SiO2 catalysts with 5 wt.% of Ru were also compared as showed in Supplementary Fig. 2. Both Ru/SiO2 and Na-Ru/SiO2 catalysts showed promising stability within 50 h of test. To better illustrate the outstanding FTO catalytic performance of Na promoted Ru-based catalyst, the preparation method was optimized, and a Na-2%Ru(P)/SiO2 catalyst with a relative lower Ru loading amount was prepared for FTO evaluation. Polyvinylpyrrolidone (PVP) was used during catalyst preparation procedure to greatly increase the Ru metal dispersion with higher exposed metallic surface area. It was found that the Na-2%Ru(P)/SiO2 catalyst showed high stability for 500 h, and olefins selectivity kept in the range of 75~80% while that of undesired C1 by-products was always suppressed within 5%.
In the revised manuscript, the stability test of Ru/SiO2 and Na-Ru/SiO2 catalyst was added as Supplementary Fig. 2 in the Supplementary Information, and the corresponding explanation was added in the main text as following: "Furthermore, stability test was carried out as shown in Supplementary Fig. 2. The catalytic performance for both Ru/SiO2 and Na-Ru/SiO2 catalysts remained stable within 50 h of test. Especially, the Na-2%Ru(P)/SiO2 catalyst with much lower Ru loading amount (1.8 wt.% Ru, ICP) exhibited high stability for 500 h without any significant loss in activity and selectivity. Overall, the activity remained at around 0.700 molCO·gRu -1 ·h -1 with intrinsic TOF of 0.210 s -1 , and olefins selectivity in total products kept in the range of 75~80% while that of undesired C1 by-products was always suppressed within 5% ( Fig.1E and Supplementary Fig. 3)

In FTS and FTO processes, product selectivity is dependent on conversion so product selectivity should be compared at similar conversion levels. For Co-based and Ru-based catalysts, CH4 selectivity is shown to increase when CO conversion
is >80 % (Yang et al. 2014, 10.1016/j.apcata.2013.10.061). Conversion results should be added to Figure 1 and S3 to demonstrate that the lower C1 selectivity attained by Na-Ru/SiO2 was not due to a difference in conversion.
Author reply: We gratefully appreciate for your professional comment. We have added CO conversion results in Figure 1 and Supplementary Fig. 6. To better illustrate this issue, we compared the product selectivity of Ru/SiO2 and Na-Ru/SiO2 catalysts under similar high CO conversion level ( Supplementary Fig. 5). It was found that a lower C1 selectivity (7.4%) was still maintained even at high CO conversion for Na-Ru/SiO2, demonstrating that the low C1 selectivity attained by Na-Ru/SiO2 was not due to a difference in conversion.
In the revised manuscript and supplementary information, Fig. 1C, 1D and S6 were replaced by revised figures. And Supplementary Fig. 5 was added in the revised supplementary information. The following sentences were also added into the revised manuscript: "Furthermore, the product selectivity was compared at similar conversion levels, as shown in Supplementary Fig. 5. Under similar CO conversion of ~70%, the sample of Na-Ru/SiO2 still exhibited high olefins selectivity of ~76% with suppressed C1 byproducts, while a large amount of paraffins with selectivity of ~76% were produced over Ru/SiO2 case." Author reply: We gratefully appreciate for your professional comment. According to the suggestion of reviewer, HAADF-STEM images and EDX elemental mapping of the spent Ru/SiO2 and 2Na-Ru/SiO2 catalysts were included into the Supplementary Fig.   11. The loading of Na was also measured by ICP-OES and the result was added as Supplementary Table 7.
Based on various characterization, the introduction of Na greatly improved the dispersion of Ru NPs. Specially, the Na promoter was homogenously distributed on both the SiO2 support and Ru NPs. In addition, a higher density of Na promoter can be clearly identified as increasing Na loading amount. We agreed with the reviewer that the electronic interaction could be strengthen by increasing the close contact of Na and NPs. However, it is still difficult to tailor the location of Na and it is a great challenge to quantify the amount of Na on the support or on Ru NPs. In addition, sodium migration may happen under FTO working conditions. Whereas, a high Na density for Na-Ru/SiO2 with increasing Na loading and its homogeneous distribution increased the chance of close contact of Na and Ru NPs.
In the revised manuscript and supplementary information, we have added the HAADF-STEM images and EDX elemental mapping for the spent Ru/SiO2 and 2Na-Ru/SiO2 in Supplementary Fig. 11. The ICP-OES results were also added in the Supplementary Table 7.  In the revised manuscript, the following sentences were added.
"Furthermore, we found that the introduction of Na greatly improved the dispersion of Ru NPs. Specially, the Na promoter was homogenously distributed on both SiO2 support and Ru NPs. A higher density of Na promoter can also be clearly identified as Na loading amount increases (Supplementary Fig. 11)." Author reply: We gratefully appreciate for your professional comment. We agree with the review that the linear characteristic of ASF distribution can be obtained over surface carbide/bulk carbide/CO insertion mechanisms. According to the suggestion of reviewer, we have thoroughly read the references of the group of de Jong (Science, 2012, 335,835) and the group of Hensen (Catal. Sci. Technol., 2014,4, 3129;Angew. Chem. Int. Ed. 2014, 53, 12746). Overall, FTS reaction mechanism is rather complex, and many uncertainties exist on the nature of the reaction intermediates. In the future work, comprehensive density functional theory study and advanced in-situ and timeresolution characterization techniques should be combined together to reveal the nature of the reaction intermediates and reaction mechanism. Based on the DFT study, the group of Hensen pointed out that the surface carbide mechanism explains the formation of long chains hydrocarbon on the stepped Ru surface, while methane would be the 25 primary hydrocarbon within the CO insertion mechanism. The lower methane selectivity and higher chain-growth-probability indicated that the surface carbide mechanism may be suitable for the Ru-based catalysts in this work.

Line
To avoid the misunderstanding, the following sentences were revised as follow: "Based on the linear characteristic of ASF distribution and the higher chain-growth probability (α) as well as the ultralow CH4 selectivity, it can be inferred that the both i.e., Na, to the Ru/SiO2 catalyst slightly increased the CO2 selectivity. Such phenomenon is commonly observed over metallic Co-based catalysts, where the alkali metal doping also slightly increased CO2 selectivity (Ind. Eng. Chem. Res. 2004, 43, 2391-2398Catal. Today, 2013, 215, 60;Appl. Catal. B: Environ., 2018, 230, 203).
In the revised manuscript, we have clarified that the CO2 selectivity increased with Na promotion and the possible explanation was also added. In addition, the nature role of Na on CO2 selectivity deserves a continuous and in-depth studies, and we will clarify it in the next research work by combining in-situ characterization techniques and DFT calculation.
In the revised manuscript, the following sentences and figure were revised and added: "In view of the ultralow intrinsic WGS reactivity of metallic Ru, we inferred that the Na-promoted Ru catalyst with metallic Ru as active phase possessed similar property. To verify this viewpoint, a WGS reaction probe experiment was performed as shown in Supplementary Fig. 21." "Furthermore, the Na doping also slightly increased CO2 selectivity for Ru/SiO2 catalyst (Fig. 1F) Author reply: We gratefully appreciate for your valuable comment. According to the suggestion of reviewer, in order to fulfill the requirements of plug-flow conditions (reactor inner diameter >10 times catalyst particle sieve fraction, catalyst bed height >50 times catalyst particle sieve fraction), the evaluation test in pilot-scale fixedbed reactor was repeated with smaller particle size. Na-2%Ru(P)/SiO2 catalyst with particle size of 12 -20 mesh (0.85 -1.7 mm) was loaded into a pilot-scale fixed-bed reactor (internal diameter: 19 mm; length: 1180 mm) for FTO reaction. The identical catalyst was also evaluated in the microreactor.
Under the reaction conditions of 538 K, 1.0 MPa, 3000 mL·gcat. -1 ·h -1 , H2/CO ratio of 2, the Na-2%Ru(P)/SiO2 catalyst showed 47.7% of CO conversion with 73.2% of olefins selectivity and < 5% of C1 by-products in a microreactor. When being evaluated in a pilot-scale reactor, the same catalyst exhibited similar catalytic performance, which showed 40.5% of CO conversion with 72.5% of olefins selectivity. The total selectivity of C1 by products including CH4 and CO2 was still less than 5%. This result suggests that the Na-2%Ru(P)/SiO2 catalyst shows a promising industrial application. 28 In the revised manuscript, the relevant parameters were revised in the industryrelevant testing of Methods section. And the corresponding catalytic data and Figure   were replaced and the following sentences were added. Reaction conditions: 538 K, 1.0 MPa, 3000 mL·gcat. -1 ·h -1 and H2/CO ratio of 2.

"Supplementary Notes:
The Na-2%Ru(P)/SiO2 catalyst was evaluated in a pilot-scale reactor (12 -20 mesh) and microreactor (40 -60 mesh), respectively, under reaction conditions of 538 K, 1.0 MPa, 3000 mL·gcat. -1 ·h -1 , H2/CO ratio of 2. As shown in Supplementary Fig. 23, the olefins selectivity in total products reached up to 72.5% while the sum selectivity of undesired CH4 and CO2 was suppressed within 5% at CO conversion of 40.5% and TOF of 0.312 s -1 in the pilot-scale reactor, which is very similar to that in microreactor. The CH4 selectivity for both reactors was much lower than the value predicated by the  classic ASF model. Moreover, a chain-growth probability at around 0.76 was obtained in both pilot-scale reactor and microreactor, demonstrating the as-obtained catalyst is very suitable to produce long-chain olefins. In addition, a similar hydrocarbon distribution was also obtained, confirming that the pellet Na-2%Ru(P)/SiO2 catalyst shows a promising industrial application with high olefins yield and low fraction of undesired C1 by-products." Author reply: We gratefully appreciate for your kind reminder. We have corrected them in the revised manuscript.

Experimental methodology for x-ray spectroscopies is missing?
Author reply: We gratefully appreciate for your kind reminder. The experimental methodology for x-ray spectroscopies was added in the revised manuscript as following.
"X-ray absorption fine structure (XAFS) data was performed at the BL14W1 of Shanghai Synchrotron Radiation Facility (SSRF), China. The storage ring of the SSRF was operated at 3.5 GeV with a maximum current of 230 mA. All data was acquired at the Ru K-edge in transmission mode. X-ray absorption near-edge spectroscopy (XANES) and extended X-ray fine-structure (EXAFS) spectroscopy of samples were collected under ambient condition using a fixed-exit double-crystal Si (111) monochromator. Catalyst sample was pressed into pellets within LiF, and then placed inside a stainless steel in situ cell which was surrounded by a heater. Reduction of the Na-Ru/SiO2 catalyst was carried out by heating the in-situ cell at 10 K/min in the following pure H2 up to 573 K, during which the XAFS spectra were measured at 298 K, 423 K and 573 K, respectively. Then the reduced Na-Ru/SiO2 catalyst was treated by syngas (H2/CO=2) in the in-situ cell at 533 K for 30 min and the XAFS spectra was collected. The data analysis was performed using IFEFFIT software package according to standard data analysis procedures 34 . The energy was calibrated by collecting spectra